Reliable corrosion monitoring is important to reduce physical failures of components and reduce production costs and delays. Various attempts have been made using electrochemical (EC) and non-electrochemical techniques to identify corrosion processes. For example, linear polarization resistance (LPR) and electrochemical noise methods have been used to identify corrosion rates, types of corrosion, and parameters associated with localized corrosion. Other techniques include the application of electrical resistance (ER) measurements to determine loss of thickness and hence determine corrosion rates. However, these methods have not been entirely satisfactory in providing an unambiguous method to determine the propagation of localized corrosion in a robust and cost effective manner.
One of the problems encountered with currently available corrosion monitoring methods and devices is the lack of reliable measurements to determine uniform corrosion rate or the rate of localized corrosion. The LPR technique typically only provides information on uniform corrosion conditions because it provides an average signal for the surface of the electrode being monitored. Depending upon the environment, metallic material, and corrosion type, the assumption that the corrosion rate is proportional to the measured charge transfer or polarization resistance is invalid when the corrosion is of a localized nature. It is known that localized corrosion (e.g., pitting) is a leading cause of physical and/or mechanical failure. With LPR, the instantaneous corrosion rate may vary by several orders of magnitude over a short time. Moreover, due to the complex nature of the measurements and varying resistances involved, the rate at which the potential is scanned may have a significant effect on the amount of current produced. Such systems require precise measurements of small incremental changes in the electrical properties of the sensor device, thus making them quite susceptible to inaccuracy due to noise. Accordingly, such devices typically require relatively complex and expensive components to overcome the noise problems, substantially increasing the cost of making and using such devices.
A drawback of EC-type sensors is their considerable bulk due to the long length of the exposed strip necessary to make changes in resistance easily measurable. Although it may be possible to reduce the thickness of the strip, this will adversely affect the life of the sensor because a reduced sensor thickness will corrode in a shorter period of time.